First campervan road trip, June 2023. I'd done zero calculations. A 500 Wh station, a dodgy fridge, a 100 W panel stuck on the roof. Result: by day three, my station was stone dead by 2pm. Fridge off. Phone dead. And me, stranded in a supermarket car park in Dorset, hunting for a mains socket like an energy beggar. All because I hadn't spent ten minutes with a pen and paper doing a consumption audit.
This guide is the ten minutes I should have taken before setting off.
Before you know how many watts you need, you have to know how many watts you actually use. Not in theory. In practice, with your gear, your habits, your way of living in your van.
The formula is simple. For each appliance, multiply its power in watts by the number of hours you use it daily. That gives you its daily consumption in watt-hours (Wh). Add everything up. That's your daily requirement.
But watch out: the power printed on an appliance label is usually the maximum power. Your 45 W fridge doesn't consume 45 W non-stop. The compressor cycles on and off: 15 minutes on, 30 minutes off, depending on ambient temperature and the thermostat setting. In practice, a 45 W fridge uses between 15 and 25 W on average. It's this average power that counts for your calculation.
I'm taking a classic campervan build -- a Fiat Ducato, Mercedes Sprinter, or similar -- with a mid-range fit-out. Here's what most campervan owners plug in daily.
The compressor fridge. This is your biggest consumer. A Dometic CFX 35W or equivalent draws between 15 and 25 W on average depending on outside temperature. In hot weather (30 degrees C outside), the compressor runs more often and the average climbs to . In cooler weather (15 degrees C), it drops to . Over 24 hours, that's between . Let's call it for a standard summer day.
25 W12-15 W360 and 600 Wh480 WhLED lighting. Two or three interior LED strips draw 5 to 10 W total. Used for about 4 hours a day (evening + morning), that's 20 to 40 Wh. Nothing to worry about.
Your phone. A full charge for a modern iPhone or Samsung is roughly 15 to 20 Wh. If you charge two phones a day, budget 30 to 40 Wh.
The laptop. A MacBook Air draws between 30 and 60 W depending on workload. For 3 hours of work, that's 90 to 180 Wh. If you work remotely from your van, this is a significant chunk.
The fan. A Maxxfan or equivalent draws between 3 and 30 W depending on speed. At medium speed, say 10 W for 8 hours overnight in summer: 80 Wh.
The water pump. 30 to 60 W, but it only runs a few minutes per day. Total: 5 to 15 Wh. Negligible.
The diesel heater (Webasto or a Chinese diesel unit). Good news: the diesel combustion provides the heat -- electricity only powers the control electronics and the blower fan. Electrical consumption: 10 to 30 W depending on the setting. On a cold night over 10 hours: 100 to 300 Wh.
Drone or camera battery charger. Highly variable. A DJI Mini battery is 20 Wh. A Mavic 3 is 77 Wh per battery. Three batteries: 230 Wh. Not trivial.
The 4G/5G router or mobile hotspot. 5 to 15 W running constantly. Over 24 hours if you leave it on: 120 to 360 Wh. A lot of people forget this one entirely.
"Minimalist" profile: fridge + lighting + phones. You live outdoors during the day and head back to the van in the evening to sleep. Daily consumption: 500 to 600 Wh.
"Comfort" profile: fridge + lighting + phones + laptop 2h + fan overnight. The standard campervan owner who works a bit, cooks a bit, and enjoys a lot. Daily consumption: 700 to 900 Wh.
"Mobile office" profile: fridge + lighting + phones + laptop 6h + fan + permanent 4G router + charging various batteries. The hardcore digital nomad who works from the van. Daily consumption: 1000 to 1400 Wh.
These figures aren't pulled from a theoretical table. They come from my own experience across three years of part-time van life and feedback from the community.
You know your daily consumption. Now, how many days of autonomy do you want without any recharging?
One day of autonomy is the bare minimum if you're counting on solar to top up each day. Two to three days is comfortable -- enough to ride out a rainy day or a shaded parking spot without stress. Five days or more is for those heading to remote spots with no guarantee of sunshine.
For the "comfort" profile at 800 Wh per day with two days of desired autonomy, you need 1600 Wh of usable capacity. Accounting for never discharging below 10% and the inverter eating 10-15% in conversion, you need a station with roughly 2000 Wh of rated capacity.
For the "minimalist" profile with two days of autonomy: 1200 to 1500 Wh rated capacity.
For the "mobile office" profile with two days of autonomy: 2500 to 3000 Wh. That's heavy artillery territory -- a Bluetti AC200L with extension batteries or a Jackery 2000 Plus.
Pure battery autonomy is one thing. But most campervan owners supplement with solar. And that changes everything.
In summer in the south of England, a 200 W panel produces on average 800 to 1000 Wh per day. Enough to cover the "comfort" profile almost entirely. If the sun's out, your station recharges during the day and you stay in near-unlimited autonomy.
In winter, in northern England or Scotland, the same panel produces 150 to 300 Wh per day. The days are short, the sun sits low, the sky is often overcast. You won't cover even half the "minimalist" profile's needs. In winter, solar charging is a supplement, not a solution.
That's why I always say: size your station to cope without any solar during the worst period of your trip, and treat solar as a bonus that extends your autonomy.
In practice, my campervan setup -- "comfort" profile -- runs on a 1000 Wh station paired with a foldable 200 W panel. In Mediterranean summer, I've got energy to spare. In November in Cornwall, I need to find a mains socket every other day. The compromise works for me because I don't live in my van full-time. Someone who does would want to double those capacities.
We've talked about capacity (how many Wh) but there's a second parameter that catches campervan owners out regularly: instantaneous power output in watts.
Your fridge draws 45 W cruising but pulls 120 W when the compressor kicks in. If your station only outputs 100 W, the fridge won't start. It's that simple and that infuriating.
A manual pump espresso machine: 800 to 1200 W. A kettle: 1000 to 2000 W. A hairdryer: 1000 to 2200 W. A toaster: 800 to 1000 W. Anything that heats draws enormous power.
My advice: if you only want the fridge, USB charging, and lighting, a station with 500-600 W output is fine. If you want a morning coffee from an electric cafetiere or a small cooking appliance, aim for 1000 to 1500 W minimum. And if you want a hairdryer or an emergency heater, you'll need 2000 W or more.
Mistake number one: buying an enormous station to compensate for zero solar provision. If you've got 3000 Wh of battery but no solar panel, you might last four days, then you're flat and facing six hours plugged in at a campsite. Better to have 1500 Wh with a solid 200 W panel that keeps you self-sufficient day to day.
Mistake number two: forgetting the fridge at night. The fridge runs 24 hours a day. Not 8 hours. Not 12 hours. Twenty-four. It's routinely the most underestimated item because you don't see it consuming.
Mistake number three: not measuring before buying. A plug-in power metre costs £12. Plug each appliance into it for 24 hours and note the actual consumption. Manufacturer specs fib or round up. The power metre doesn't.
Mistake number four: ignoring the efficiency chain. Energy from the panel passes through the MPPT controller (5% losses), gets stored in the battery (5-8% losses in charge/discharge), then goes through the inverter for AC appliances (10-15% losses). In total, between the panel and your appliance, you lose 20 to 25% of the energy. Your 200 W panel doesn't put 200 Wh per hour into your fridge. It delivers 150 to 160 Wh.
Grab a piece of paper. Write down each appliance, its average power (not max), and its hours of use. Multiply. Add up.
Fridge: 20 W x 24 h = 480 Wh.
Lighting: 8 W x 4 h = 32 Wh.
Phones: 40 Wh (two charges).
Laptop: 45 W x 3 h = 135 Wh.
Fan: 10 W x 8 h = 80 Wh.
Miscellaneous (pump, router, etc.): 50 Wh.
Total: 817 Wh per day.
Recommended station for 2 days of autonomy: 817 x 2 = 1634 Wh usable, meaning roughly 2000 Wh of rated capacity.
Recommended solar panel to cover daily needs in summer: 200 to 300 W.
Adjust with your own figures. If you don't have a laptop, you drop to 680 Wh. If you add a diesel heater overnight in winter, you climb to 1100 Wh or more.
Sizing isn't an exact science. It's a common-sense calculation with a safety margin. Take your result, add 20%, and you're sorted. Better to have a bit too much than not enough. Because running out of power in a supermarket car park in Dorset at 2pm in June -- trust me, that's not an experience you want to repeat. For more detail, have a look at my portable power station guide and my explanation of the watt-hour -- they'll help you make sense of the numbers.
A compressor fridge like a Dometic CFX 35 averages 15 to 25 W (not the 45 W on the spec sheet, because the compressor cycles). Over 24 hours, that's between 360 and 600 Wh depending on the heat. It's your biggest single consumer, and the one most often underestimated.
Both work, but the portable station has a massive advantage: you can unplug it and take it with you. No permanent wiring, no vehicle modifications, and if you change vans, it comes along. A hardwired auxiliary battery is more discreet and charges while you drive, but it's a proper job to install and it stays with the vehicle.
For a decent setup (1000 Wh station + 200 W panel on the roof + cabling), budget £850 to £1,500 all in. It's an investment, but it pays for itself in a few months of free wild camping without paying for pitches.
Not necessarily, but it's a serious comfort upgrade. Your auxiliary battery handles the 12V side (lighting, water pump), while the station manages the 230V side (laptop, coffee maker, chargers). The two complement each other beautifully. And if one fails, you've always got the other as backup.
Cedric